Whenever you place a bobbin into your bobbin case, give it a little tap. The bobbin should have some bounce to it. If it doesn’t, your bobbin case check spring may have lived its life and will need to be replaced. It is certainly more cost efficient to just replace the spring over buying a whole new bobbin case. It is always a good idea to have an extra bobbin case check spring on hand. To install it, just take a small flat blade screwdriver and pop out the old one. This new one will snap right back in.